Detectors for emitting audible sounds when radiation impinges on or passes through their detection elements are well known to those working in environments where nuclear radiation can be hazardous. One of the earliest of such counters is the Geiger-Muller (G-M) counter which utilizes a gas filled tube. When one of the molecules of the gas in the tube encounters a gamma ray, it is ionized. The tube wall is the cathode while a positive central wire is the anode, the latter collecting the ionized electrons. The electrical pulse produced from the anode is passed through an amplifier and a speaker to produce an audible indication when radiation is encountered. Existing pocket chirpers use G-M tubes as described above. The electronics accompanying such tubes must amplify the pulses coming from the tubes before applying that signal to an integration circuit that measures the amount of radiation received. After a preselected amount of radiation has been received, the device discharges to an audible sound producing apparatus such as a speaker to give a chirp which indicates to the wearer that the given or selected amount of radiation has been encountered.
G-M tubes have two main drawbacks which are solved by the present invention. First, a gas-filled G-M tube has a low density and therefore requires a relatively large detection volume to achieve adequate sensitivity for normal low radiation fields. The cadmium telluride crystal of the invention, to the contrary, has a density of about 6.2 g/cc. For gamma ray and x-ray detectors this is a very high density and may be compared to iron, which is not a detector, but which has a density of 7.9 g/cc. Therefore, it can be seen that a very small CdTe crystal will have the same sensitivity as a much larger volume G-M tube. This illustrates that the invention greatly reduces the necessary size of an instrument for detecting radiation for the above-noted purpose. Second, the G-M tube requires a relatively high voltage supply, i.e., at least about 200 volts and higher, depending on the particular tube to be used. The CdTe crystal detector in accordance with the present invention, requires only a few volts that can be obtained directly from a small inexpensive battery. No high voltage electronic circuitry is necessary, thereby reducing circuit size, circuit complexity, and battery power requirements. It will also be appreciated by those skilled in the art that very poor energy resolution CdTe crystals can be utilized in the invention; after all, the G-M tubes presently used for such purposes possess no energy resolution at all. Therefore, poor quality CdTe crystals can be used in practicing the invention instead of the much more expensive high energy resolution crystals normally used for gamma ray spectroscopy purposes. A use therefore exists for normally unmarketable poor quality CdTe crystals.